In conventional tennis rackets, the head and throat portions of the frame are more or less of a uniform height, typically about 19 mm for a graphite frame, the term "height" referring herein to the dimension perpendicular to the plane of the racket strings. The height of the shaft portion may or may not be the same as the head and throat, but in any event a handle is formed on the shaft which has a larger dimension.
When the ball is hit, the resulting impact produces bending in the racket frame, about the handle where the racket is gripped. The amount of racket deflection depends upon the particular racket construction, e.g. cross-sectional shape and thickness, as well as the materials used. Variations of dimension or wall thickness, at different areas of the frame, can also affect the bending profile. Thus, a frame having a uniform cross-section produces a characteristic bending profile at various longitudinal positions along the frame. Recently, several rackets have been introduced which vary the height of the frame along the racket so as to alter this characteristic profile in various ways.
Kuebler U.S. Pat. No. 4,664,380 discloses several racket configurations in which the height of the frame is greatest in the throat area i.e., the middle portion of the racket, decreasing toward the top of the racket. The height in the throat area is also greater than the height of the racket handle. As described by Kuebler, increasing the height in the throat, as opposed to a conventional, uniform height frame, moves the center of percussion of the racket so as to match the vibration frequency of the racket to that of the ball.
Other rackets, such as the Revolutive Apollo, as well as rackets sold by Donnay, Vokyl, and Head use thinner and thicker sections along the racket so as to move the centers of vibration and change the response of the racket. These rackets then attempt to improve the power performance and response.